Question

Explain the following: Removal of iron and manganese

Answer 1

When combined levels of iron and manganese exceed 10 mg/L, the most effective treatment involves oxidation followed by filtration. In this process, a chemical is added to convert any dissolved iron and manganese into the solid, oxidized forms that can then be easily filtered from the water.

Answer 2

Iron and manganese control is the most common type of municipal water treatment in
Minnesota. Iron and manganese occur naturally in groundwater. Neither element causes adverse
heath effects at concentrations typically found in Minnesota. These elements are, in fact,
essential to the human diet.
Water containing excessive amounts of iron and manganese can stain clothes, discolor plumbing
fixtures, and sometimes add a “rusty” taste and look to the water. Surface water generally does
not contain large amounts of iron or manganese, but iron and manganese are found frequently in
water systems that use groundwater.
The Safe Drinking Water Act secondary standards (aesthetic, not health related) for iron in
drinking water is 0.3 parts per million (ppm) and 0.05 ppm for manganese. If water contains
more than 0.05 ppm iron, or 0.01 ppm manganese, the operator should implement an effective
hydrant-flushing program in order to avoid customer complaints.
BACTERIA AND IRON AND MANGANESE
Iron and manganese in water also promote the growth of bacteria (including iron bacteria). These
organisms obtain energy for growth from the chemical reaction that occurs when iron and
manganese mix with dissolved oxygen. These bacteria form thick slime growths on the walls of
the piping system and on well screens. These shines tend to be are rust-colored from iron and
black-colored from manganese. Variations in flow can cause these slime growths to separate
from pipe walls, resulting in dirty water in the system.
The growth of iron bacteria can be controlled by chlorination. However, when water containing
iron is chlorinated, the iron is converted from the ferrous state to the ferric state--in other words,
rust--and manganese is converted into black manganese dioxide. These materials form a coating
on the inside of the water main and, when they break loose, a customer will sometimes complain
of “dirty” water.
Iron bacteria will use even small amounts of iron present in the ferrous state, oxidize it, and then
use the energy. Manganese is also used by other bacteria to form organics, which contribute to
the iron bacteria slime in the well and/or water system.
Iron bacteria are found any where a food source of iron is available. The presence of one
bacterium is all that is needed to start an infestation in a well or a distribution system.
IRON AND MANGANESE CONTROL
Methods to control iron and manganese in distribution systems include arranging for alternate
water sources, adding phosphate to the water to keep iron and